In relation to a radio communication system including a radio base station unit (eNB) and a plurality of terminals each of which has a repeating function (hereinafter called simply “repeaters”), there has already been proposed cooperative relay called Coded Cooperation in order to yield a receiving diversity effect at the eNB. Coded cooperation is a relaying scheme by means of which information that respective repeaters desire to transmit are exchanged and by means of which information that a repeater of interest and another repeater desire to transmit is also transmitted to the eNB. The Coded Cooperation is hereinbelow referred to simply as “cooperative relay.”
FIG. 9 shows example operation (a successful example) of cooperative relay. Descriptions are provided while attention is paid to operation of Repeater 1 (hereinafter described as a “repeater 1”) in FIG. 9. The repeater 1 divides data into first transmission data S1 including systematic bits and parity data P1 including parity bits; transmits the first transmission data S1 to Repeater 2 (hereinafter described as a “repeater 2”); and receives first transmission data S2 from the repeater 2.
The repeater 1 generates parity data P2 from the received first transmission data S2. Subsequently, the repeater 1 transmits the first transmission data S1 of itself to the eNB and subsequently transmits the generated parity data P2 to the eNB.
Likewise, operation of the repeaters 2 is described. The repeater 2 divides data into the first transmission data S2 including systematic bits and parity data P2 including parity bits; transmits the first transmission data S2 to the repeater 1; and receives the first transmission data S1 from the repeater 1.
The repeater 2 generates the parity data P1 from the received first transmission data S1. Subsequently, the repeater 2 transmits first transmission data S2 of itself to the eNB and subsequently transmits the generated parity data P1 to the eNB.
In doing so, the eNB receives data, which are divided into two blocks, from each of the respective repeaters by way of respective different paths (cooperative relay is performed), so that a diversity effective can be yielded. Moreover, in a case where a level of one path remains low for a long period of time for reasons of fading of a long period (slow fading), it becomes possible to avoid occurrence of a situation in which receiving operation becomes impossible.
However, as can be seen from (unsuccessful) example operation of cooperative relay shown in FIG. 10, there has been a problem of, when one repeater or both repeaters are unsuccessful at exchanging data between the repeaters (occurrence of CRC NG, or the like), data to be transmitted after transmission of first transmission data from a repeater of interest becoming extinct.
There are available the following two simple countermeasures against a case where exchange of data between repeaters is unsuccessful.
(1) Transmit parity data of itself (see; for instance, Patent Document 1)
(2) Introduce an ACK signal and an NACK signal.
Patent Document 1: US 2003/0148732 A